Contemporary piezoelectric actuators are found in two basic configurations, operating in what are commonly known as the D33 and D31 modes. The relative displacement in the D33 mode is about three times greater than in the D31 mode. A D33 mode piezoelectric actuator is typically composed of a stack of piezoelectric components. Displacement in the D33 mode is an expansion in the same direction as both the electric field and the poling direction. D33 mode actuators provide a linear motion. A D31 mode actuator acts by contracting perpendicular to the electric field and the poling direction.
The D33 mode piezoelectric actuators are more commonly seen in industrial applications. They use the expansion of the active material, in D33 mode to produce a displacement. Typically, the active part of these actuators includes a stack of ceramic layers ranging in thickness between 20 to 100 micrometers (μm), separated by thin, uniformly sized and shaped metallic layers known herein as electrodes. The actuator deformation is often 0.15% (15 μ/cm) of the total unit size.
The D31 mode actuators use the contraction of the active material, in the D31 mode, to produce a negative displacement. The active material of these actuators also includes ceramic layers separated by thin metallic layers. However these D31 mode actuators displace perpendicular to the electric field and the poling direction, with the displacement being a function of the length of the actuator, with the number of parallel layers determining the stiffness of these piezoelectric actuators. These actuators can and do bend, but when short, do not bend very much and may require higher potential differences to achieve these results.
What is needed is a piezoelectric actuator combining the advantages of the D33 mode actuator in terms of displacement and the consequent lower voltage driving requirements, with the flexibility of bending found in the D31 mode piezoelectric actuators.